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NDA 2021
Exam
NDA
Year
2021
Subject
Mathematics
Chapter
Permutation and Combination

NDA 2021 · Mathematics · Permutation and Combination

Consider the digits 3,5,7,9 . What is the number of 5 -digit...

Consider the digits 3,5,7,93,5,7,9. What is the number of 5 -digit numbers formed by these digits in which each of these four digits appears?

Options

  1. A240
  2. B180
  3. C120
  4. D60

Correct answer

A. 240

Step-by-step solution

Given digits are 3, 5, 7,9. ∴\therefore The number of 5 -digit number formed by these digits in which each of these four digits appears =4C1×5!2!=4⋅5⋅4⋅3⋅2!2!=240={ }^4 C_1 \times \frac{5!}{2!}=4 \cdot \frac{5 \cdot 4 \cdot 3 \cdot 2!}{2!}=240
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